High-resolution observations of dissolved isoprene in surface seawater in the Southern Ocean during austral summer 2010-2011

We measured dissolved isoprene (2-methyl-1,3-butadiene; C5H8) concentrations in a broad area of the southern Indian Ocean and in the Indian sector of the Southern Ocean from 35A degrees S to 64A degrees S and from 37A degrees E to 111A degrees E during austral summer 2010-2011. Isoprene concentrations were continuously measured by use of a proton-transfer-reaction mass spectrometer combined with a bubbling-type equilibrator. Concentrations of isoprene and its emission flux throughout the study period ranged from 0.2 to 395 pmol L-1 and from 181 to 313 nmol m(-2) day(-1), respectively, the averages being generally higher than those of previous studies. Although we found a significant linear positive relationship between isoprene and chlorophyll-a concentrations (r (2) = 0.37, n = 36, P < 0.001), the correlation coefficient was lower than previously reported. In contrast, in the high-latitude area (> 53A degrees S) we identified a significant negative correlation (r (2) = 0.59, n = 1263, P < 0.001) between isoprene and the temperature-normalized partial pressure of carbon dioxide (n-pCO(2)), used as an indicator of net community production in this study. This suggests that residence times and factors controlling variations in isoprene and n-pCO(2) are similar within a physically stable water column.